There is a considerable interest in methods and apparatus for detection, measuring and monitoring chemical properties of a substance. Apparatus for detecting the presence of a substance based on the detection of acoustic waves have received increasing interest in recent years in a wide range of applications. They can, for example be used as resonators, filters, sensors and actuators.
Experimental configurations have relied on expensive commercial test equipment such as spectrum/network analyzers, fixed oscillators and vector voltmeters. Together with this, separate liquid flow systems requiring external computer control, restrict the experiment environment and impose specialized experimental test procedures. The development of a fully portable, stand alone acoustic wave (AW) sensor system that encompasses both the sensor data acquisition and liquid flow systems is seen as a positive and exciting advancement in the development of AW sensors. However, the majority of reported work to date on AW sensors has ignored the optimization of the overall sensor configurations for the development of portable instrumentation for the detection of very low concentrations of target analyte.
U.S. Pat. No. 4,361,026 describes a method and an apparatus for sensing fluids using acoustic waves. The apparatus describes a completely integrated sensor. A disadvantage of this sensor is the high manufacturing cost of the sensor. In, for example, medical applications, one is mostly interested in single-use devices. Moreover, the ""026 patent does not allow for quick changes in the sensor geometry without changing the overall sensor configuration.
This will result in a high cost for each sensor. The sensor described in the ""026 patent is based on a standard SAW delay line onto which a sensitive and selective film is deposited. The design is intended to work at the design frequency exclusively, and no disposability has been contemplated. Furtheron, the sensor is based on surface acoustic modes exclusively, which does not make multilayer propagation possible.
Another patent in the art is U.S. Pat. No. 4,312,228 which describes a method and an apparatus for the monitoring the physical parameters relating to various fluids and polymers based on acoustic waves. Physical parameters relating to fluids are investigated by contacting the fluid with a coating on the surface of a piezoelectric material unit. The coating on the piezoelectric substrate is selective to the interaction with the fluid to detect. The sensor is very bulky. The coating is applied directly on the piezoelectric substrate, resulting in a lower sensitivity towards the substance. The ""228 patent has the same disadvantages as recited above and moreover, the piezoelectric substrate is coated directly with a selective film. This results in a lower sensitivity. The ""228 patent is focused on the description of the liquid cell for the sample delivery.
The present invention is directed to overcome the above mentioned problems.
The aim of this invention is to provide an apparatus for sensing the presence of a substance. Another aim of the invention is to provide an apparatus for sensing the presence of a substance that can be manufactured easily, cheaply and single-use focused on a variety of substrates. Yet another aim of the invention is to provide an apparatus for sensing the presence of a substance that is low cost, h as a fast response, has a simple experimental procedure, is portable, is small in size and has a high sensitivity.
The apparatus comprises two parts which are removably fixable such that first part is in close contact with second part during the working of the device. In a first aspect of this invention, an apparatus is disclosed for detecting the presence of a substance using acoustic waves comprising a first part for generating acoustic waves and a second part comprising a sensing and acoustic wave guiding device for sensing said substance and for propagating said acoustic waves. Said sensing and acoustic wave guiding device can, but is not limited to, comprise a sensing layer for sensing said substance and an acoustic wave guiding layer for propagating said acoustic waves. Said sensing layer is for sensing said substance. Preferably said acoustic waves are surface acoustic waves. Acoustic wave guiding layer propagates said acoustic waves. In this first aspect of the invention, said first part is removably fixable to said second part so that when fixed said acoustic waves propagate in said second part. Said first part can contain, but is not limited to, a piezoelectric substrate. The acoustic wave guiding layer should be capable of supporting acoustic wave propagation. Besides this, the acoustic wave guiding layer is chosen such that it confines the acoustic waves energy at the sensor surface, rendering it highly sensitive to surface perturbations. In order for the acoustic energy to be confined in the guiding layer, it is preferable that the acoustic velocity for the material of the guiding layer be smaller than the acoustic velocity for the substrate. By selecting the appropriate acoustic wave guiding layer, very low perturbations at the surface of the sensing layer can be detected. The sensing layer can be, but is not limited hereto, directly applied on the acoustic wave guiding layer. Said first part is reusable, while said second part can be chosen depending on the substance to be detected. Said second part can be manufactured easily, cheaply and single-use and is preferably made from materials which are less expensive.
In a further embodiment, said sensing and acoustic wave guiding device propagates said acoustic waves for sensing said substance. This means that a part of said guiding layer is exposed to the substance and is able to interact with the substance.
In a further embodiment of this invention, an apparatus as recited in the first aspect of the invention is disclosed wherein said first part comprises at least a piezoelectric material.
In a further embodiment, an apparatus for detecting the presence of a substance as described in the first aspect of this invention is disclosed, wherein said apparatus further comprises an electrode layer. Said electrode layer is located on said second part. Said electrode layer can be embedded in said acoustic wave guiding layer. Preferably, the electrode layer has an interdigital configuration (IDT). When the electrode layer is located on the second part, it allows for quick changes in the design of the IDTs, as they are printed on the disposable part. It also allows for changes on the frequency of operation, since the frequency is determined by the geometry of the interdigital transducers.
In an alternative embodiment, said electrode layer can be embedded in said first part.
In a further embodiment of the invention, said second part of the apparatus can further comprise a support structure located at least on top of the sensing and acoustic wave guiding device. At least a part of the sensing and acoustic wave guiding device is exposed to the substance. The support structure can be made of a material selected from the group comprising a semiconducting material, a polymer based material or an amorphous material such as glass.
In a further embodiment of the invention, said sensing layer consists essentially of a recognition layer that may be influenced by interaction with said substance. The interaction can be a chemical or a physical interaction.
In a further embodiment of the invention, said acoustic wave sensor is designed such that the acoustic waves penetrate the sensing and acoustic wave guiding device in the region where the substance interacts with said sensing and acoustic wave guiding device, such that a perturbation of the acoustic waves due to the interaction of the substance with the sensing and acoustic wave guiding device, is obtained.
In a further embodiment of this invention, said apparatus further comprises a radio frequency (RF) generator for applying an input RF signal to said electrode layer and a receiver that receives an output RF signal from said electrode layer.
In a further embodiment, said apparatus further comprises a clamping system for removably fixing said first part to said second part. Said clamping system is chosen such that the propagation of the acoustic waves from the first part to the second part is not altered.
As some of the piezoelectric substrates are used also for optical and temperature applications, such substrate also allows for the integration of various sensors on the same first part of the apparatus.